Printing head construction for use in a screen printing machine

ABSTRACT

A printing head assembly having a head frame for supporting a printing screen and having opposed guide rails for slidably supporting a squeegee carriage for traversing a printing stroke. The guide rails are adjustably supported on the head frame for affecting the adjustment of the guide rails relative to a printing surface so as to maintain the squeegee pressure substantially constant during a printing operation. The printing head assembly also includes an improved rocker or tilting assembly for alternately raising and lowering a pair of squeegees that includes an endless shifter mechanism which is connected in driving relationship with the squeegee carriage drive.

United States Patent [1 1 Jaffa May 27, 1975 [54] HEAD 3,143,961 8/1964 .Iaffa et a1. 101/123 US IN A SCREEN PRINTING MACHINE 3,650,208 3/1972 Lambert [75] Inventor: David Jaffa, Fairlawn, NJ.

[73] Assignee: Precision Screen Machines, Inc.,

Hawthorne, NJ.

[22] Filed: Apr. 3, 1973 [21] App]. No.: 347,383

[52] US. Cl. 101/123; 101/124; 101/126 [51] Int. Cl B4lf 15/42 [58] Field of Search 101/123, 124, 114, 115

[56] References Cited UNITED STATES PATENTS 2,355,930 8/1944 Thorne 101/123 2,783,709 3/1957 Thomas 101/123 2,863,382 12/1958 Giani 101/123 2,963,964 12/1960 Klump... 101/123 3,101,665 8/1963 Hall lOl/123 Primary ExaminerRobert E. Bagwill Assistant ExaminerR. E. Suter 5 7] ABSTRACT A printing head assembly having a head frame for supporting a printing screen and having opposed guide rails for slidably supporting a squeegee carriage for traversing a printing stroke. The guide rails are adjustably supported on the head frame for affecting the adjustment of the guide rails relative to a printing surface so as to maintain the squeegee pressure substantially constant during a printing operation. The printing head assembly also includes an improved rocker or tilting assembly for alternately raising and lowering a pair of squeegees that includes an endless shifter mechanism which is connected in driving relationship with the squeegee carriage drive.

8 Claims, 7 Drawing Figures PATENTEmmzmrs 3,885,493

saw 3 NIIA PRINTING HEAD CONSTRUCTION FOR USE IN A SCREEN PRINTING MACHINE PROBLEM AND PRIOR ART A screen printing head assembly for a screen printing apparatus generally comprises a frame for supporting a printing screen and an associated squeegee carriage on which one or more squeegee blades are mounted. The printing operation is generally effected by the squeegee blade traversing a printing stroke relative to the printing screen by moving one relative to the other. Accordingly the amount of pressure which the squeegee bears on the screen during a printing operation controls to some extent the amount of ink or color which is forced through the screen and onto the material to be printed. The material to be printed in turn is supported generally on a flat printing surface.

It has been frequently noted that the printing surface of a screen printing apparatus may warp and/or may not be rendered perfectly flat or level. This problem is particularly aggrevated in the larger screen printing machines wherein the printing surface covers considerable area, often extending a hundred feet or more in length.

In such installations, if the printing surface was not maintained perfectly flat, the pressure exerted by the squeegee in traversing a printing stroke would vary. This is because the squeegee would exert more pressure over the high spots of an unlevel or warped printing surface, and less pressure over the low spots. As a result the amount of color permeation and/or of color deposited on the material would vary. For this reason the resulting design would shown color variations which frequently adversely affected the quality of the finished screen print.

Also where such screen printing machines utilized a dual or chopper type squeegee assembly in which the squeegees are alternately raised and lowered, the squeegee carriage supporting such squeegee blade were heretofore required to be encumbered with considerable operating structures for activating such squeegee assembly. As the printing stroke is usually effected by traversing the squeegee blades relative to a stationary screen, the hardware required to be supported and moved with the squeege blades heretofore was quite considerable. Also were the squeegee blades were hydraulically operated considerable length of hose connections were heretofore required. In the larger installations these problems are considerably aggrevated as the distance of traverse increases.

OBJECTS It is therefore an object of this invention to provide an improved screen printing head having an adjusting feature for insuring that the pressure exerted by the squeegee blades is maintained substantially constant in traversing a printing stroke.

Another object resides in the provision of a screen printing head having an improved tilting mechanism for effecting the alternate actuation of a pair of squeegee blades.

Another object is to provide an improved printing head which is relatively simple in construction, can be readily fabricated and which is positive in operation.

Another object is to provide a printing head which can be rendered readily adjustable to the printing surface.

BRIEF DESCRIPTION OF THE INVENTION The foregoing objects and other features and advantages are attained by a printing head for a screen printing machine defined by a rigid head frame for supporting opposed guide rails on which a squeegee carriage is slidably mounted for traversing a printing stroke. The guide rails are adjustably supported on the head frame by a series of spaced adjusting fasteners so that the guide rail may readily adjust to conform to any uneveness which may occur in the printing surface of the screen printing machine. The invention further contemplates an improved tilting or rocker assembly by which a pair of squeegee blades (chopper blades) are mounted on the squeegee carriage for alternate movement between a raised and lowered position. The tilting assembly also includes an endless operating member connected to a squeegee rocker or tilt mechanism to effect the actuation thereof. The endless actuating means is connected in driving relationship with the drive of the squeegee carriage; the arrangement being such that the tilting drive is rendered operative independently of the squeegee drive, even though the two are connected in driving relationship.

FEATURES A feature of this invention resides in the provision of squeegee guide rails which can be readily adjusted to conform to any uneveness noted in a printing surface for maintaining uniform squeegee pressure during a printing stroke.

Another feature sides in the: improvement of a tilting mechanism for a pair of squeegee blades which includes an endless operator which is connected in driving relationship with the squeegee drive.

Another feature resides in. an improved squeegee blade tilting assembly which minimizes the need for encumbering the printing head with considerable operating mechanisms.

Another feature resides in an improved tilting assembly of a squeegee blade assembly in which the operating mechanism therefor need not be required to be moved over considerable distances.

Other features and advantages will become more readily apparent when considered in view of the specification and the drawings in which:

FIG. 1 is a plan view of a screen printing head having portions broken away embodying the present invention.

FIG. 2 is a side elevation view of the printing head construction of FIG. 1.

FIG. 3 is a sectional view taken through line 3-3 of FIG. 1.

FIG. 4 is a fragmentary plan view taken along line 4-4 on FIG. 3.v

FIG. 5 is a diagrammatic side elevation view illustrating the squeegee tilt or rocker assembly.

FIG. 6 is a detailed sectional view taken along line 6-6 on FIG. 2.

FIG. 7 is a detailed sectional view taken along line 7-7 on FIG. 2.

DETAILED SPECIFICATION Referring to FIGS. 1 and 2 there is shown therein a printing screen head construction 10 embodying the present invention for use on a screen printing apparams. The screen printing head 10 is generally arranged to overlie a printing surface on which a material to be printed is supported. Frequently the printing head assembly is pivotally mounted along one side to the frame of the screen printing machine for movement between a lowered operative printing position and an inoperative raised position. However, it will be understood that the printing head assembly 10, to be described, may be mounted in any suitable manner relative to the printing surface whereby it can be raised or lowered between a printing and non-printing position.

As best seen in FIGS. 1 and 2 a printing head assembly is defined by a rigid upper frame portion and a rigid loer frame portion 1 l and 12. The respective upper and lower frame portions 11 and 12 are defined by longitudinally extending side structural members 11A and 12A which are suitably secured in spaced relationship by an upright frame support 13 at the adjacent end portions.

As seen in FIGS. 3 and 6, the rigid longitudinally extending frame members 11A, 12A defining the upper and lower frame portion are illustrated as comprising a rigid tubular structural frame member 11A, 12A. End ties l4 and 15 are interconnected between the structure side members 1 1A, 12A for maintaining the longitudinally extending upper and lower structural members 11A, 12A respectively in spaced relationship. As best seen in FIG. 1, the head frame is defined by rectangularly disposed structural frame members. Connected to the lower structural frame portion 12 of the head assembly 10 is a screen support 16 for supporting thereon a printing screen, 17.

Opposed guide rails 18 are supported between the upper and lower longitudinally extending side frame members 11A and 12A of the respective head portions 11 and 12. As best seen in FIGS. 3 and 6 the respective guide rails 18 are each dependently supported from its upper longitudinally extending side frame member 11A, 11A in a manner whereby the guide rail 18 may be readily adjusted to conform to any uneveness or warpage which may occur in the surface of the printing table on which the material to be printed is supported. This is attained by supporting the respective guide rail 18, 18 from the upper structural frame member 11A by a series of spaced adjusting means 19. The adjusting means 19 are spaced along the length of the longitudinal side members 11A, 11A, preferably at approximately 6 inch intervals. As best seen in FIG. 3, the adjusting means 19 comprises a threaded adjusting rod 19A which is threaded into a tapped hole 20 formed in the top of the respective guide rails 18 and extended through appropriate apertures 22 formed in the structural side member 11A, of the upper frame portion 11. A threaded nut 23 is utilized for adjustably supporting the guide rail 18 to the respective supporting frame member 1 1A. It will thus be apparent that the guide rail 18, which is shown as a round shaft, can be readily adjusted within predetermined limits along the length thereof sufficiently to allow the guide rail 18 to conform or compensate for any uneveness or warpage occuring in the printing surface of a screen printing machine.

Slideably mounted on the opposed guide rails l8, 18 is a squeegee carriage means 24. The squeegee carriage means 24 comprises opposed carriage blocks 25 which are in sliding engagement on the opposed corresponding guide rails 18. Each carriage block 25 is similar in construction and as seen in FIG. 3 the respective carriage blocks are provided with a bearing sleeve 26 arranged to circumscribe a major portion of the circumference of the associated guide rail 18. As shown in FIG. 3, the bearing sleeve 26 circumscribes approximately 300 of circumference of the associated guide rail 18. With the construction described the respective squeegee carriage blocks 25 can readily traverse the length of the guide rail without interferring with the adjusting means 19 which dependently support the guide rail 18 from the adjacent rigid structural member 11A of the upper head frame 11. A squeegee assembly 27 is mounted between and carried on the opposed squeegee carriage blocks 25, 25 for traversing a printing stroke.

The squeegee carriage means and squeegee assembly 27 mounted thereon are reciprocally mounted in sliding relationship on the opposed guide rails l8, 18 for traversing a printing stroke.

A drive means 28 is provided for traversing the squeegee carriage means 24 and associated squeegee assembly 27 during a printing operation. As best seen in FIGS. 1 and 2 the squeegee carriage drive means 28 comprises an endless flexible drive 29 which is connected to the respective carriage blocks 25 and which is actuated by a reversible motor means 30.

In the illustrated embodiment a flexible drive 29 is disposed on opposite sides of the head frame assembly 10, each flexible drive 29 being similarly constructed. The squeegee drive means further includes a drive shaft 31 journalled on the head frame 10 adjacent one end thereof. Connected to one end of the drive shaft 31 is a sprocket or pulley 32 which is connected in driving relationship to a driving sprocket or pulley 33 connected to the output side of the motor means 30 by a flexible drive chain or belt 34.

Journalled to the opposed ends of the drive shaft are end sprockets 35, 35 about which one end of the respective flexible drive 29, 29 is threaded. The other end of the flexible drive 29, 29 is threaded about idler sprockets or pulleys 36, 36 journaled adjacent the other end of the head frame 10. The ends 29A, 29A of the flexible drive 29 are suitably connected to their respective carriage blocks 25. In operation, it will be apparent that the actuation of the motor means 30 in one direction or the other will effect the reciprocal movement of the squeegee carriage guide rails 18, 18 to effect a printing and/or flooding stroke.

The squeegee assembly 27, as best seen in FIGS. 2, 3 and 5 comprises a pair of squeegee blades 36 which are mounted on a rocker or tilting assembly or toggle means 37 whereby the squeegees 36, 36 may be alternately raised and lowered between an operative and inoperative position. Referring to FIGS. 2, 3 and 5 the tilting or toggle assembly 37 comprises a lower rocker arm 38 which is pivotally mounted intermediate the ends thereof to its respective carriage block 25. A pair of connecting links 39 pivotally interconnect the ends of the rocker arm 38 with a corresponding upper rocker member 40 which is pivoted to the carriage block 25 about pivot 41.

As best seen in FIG. 3 the pivot 42 of the lower rocker arm 38 extends through the associated block 25 and has connected to the extended end thereof an actuating lever 43. Secured to the lever 43 is a plate 448 to which the ends 44A of an endless tilting chain or cable 44 are connected.

Connected between the Corresponding pair of connecting links 39, 39 is a squeegee support bar 45 from which a respective squeegee holder 45A and associated squeegee blade 36 is supported. It will be understood that the respective squeegee blades 36, 36 may be ad justably supported from the holder 45A in a manner disclosed in prior US. Pat. No. 3,l43,96l granted Aug. 11, 1964.

An actuating means (See FIGS. 2 and 7) for actuating the rocker or toggle assembly 37 to raise and lower the respective squeegees 36 includes a pair of spaced apart lever plates 46 which are pivotally mounted to the head frame about pivot 47. Journalled about the axis of the pivot 47 is a spur gear 48 which is arranged to be disposed into meshing relationship with a complementary spur gear 49 which is connected to the head drive shaft 31. An intermediate pulley or spocket 50 is coupled to gear 48 to turn with the spur gear 48 when the latter is driven by the complementary spur gear 49.

Journalled between lever arm or plates 46, 46 and disposed on opposite sides of sprocket or pulley 50 are a pair of complementary idlers, e.g. sprockets or pulleys 51 and 52. As best seen in FIG. 2, the tilt chain or cable 44 is threaded about sprockets or pulleys 50, 51 and 52.

Disposed adjacent the opposite end of the head frame 10 are a pair of spaced upper and lower idler sprockets or pulleys 53 and 54 about which the other end of endless flexible tilt chain or cable 44 is threaded. As seen in FIGS. 2 and 5, the end of the flexible tilt chain or drive 44 is threaded over sprockets or pulleys 50 to 54 with the ends 44A, 44A connected to plate 443 of the rocker assembly.

An operating means is provided for effecting the pivoting of the lever plate 46 to alternately effect the raising and lowering of the respective squeegee blades 36, 36 whenever the means is actuated. In the illustrated form of the invention the operating means comprises a piston and cylinder assembly 56 which is pivotally mounted at one end 56A to the head frame 10. The piston rod 57 of the piston and cylinder assembly 56 is suitably connected to the lever arm 46. The arrangement is such that whenever the piston rod 57 of the piston and cylinder assembly is extended or retracted the lever plate 46 is pivoted causing the tilt chain to tilt the rocker assembly in one direction or the other to alternately raise and lower the respective squeegee blades. It will be understood that the actuation of the piston and cylinder assembly 56 is controlled by a suitable timing device so that the raising and lowering of the squeegee blades are actuated in accordance to the cycling sequence of a particular printing operation.

As best seen in FIG. 1, the squeegee carriage flexible drive 29 I is disposed on opposed sides of the head frame. Likewise the tilt chain 44 for the respective rocker or toggle means the disposed on opposite sides of the head frame, each being similar in construction. In this manner the forces exerted on each side of the squeegee carriage means and tilt means are balanced.

In operation, whenever the motor means 30 is actuated, the squeegee carriage 24 and the squeegee assembly 27 supported thereon traverse a printing stroke. In doing so, spur gear 49 on the head drive shaft 31, which is connected into meshing relationship with the complementary spur gear 48, causes the tilt chain 44 or spur gear 48 to be driven accordingly. Thus whenever it is required to effect the operation of tilting or toggle means 37 to alternately raise and lower the squeegees 36, 36 accordingly, the piston and cylinder assembly 56 is actuated to pivot the operative tilting lever 46.

By effecting the pivoting of lever plate 46 about pivot 47, the tilt chain or cable 44 is displaced to pivot the rocker lever 43 accordingly. In doing so the squeegees 36, 36 supported between the rocker assemblies 37, 37 are raised and lowered accordingly. Thus with the construction described the tilt chain or cable 44, through the interaction of complementary gears 48 and 49 is connected in driving relationship with the squeegee carriage drive chain or cable 29, permitting the squeegee carriage to traverse a printing stroke without effecting the raising or lowering of the respective squeegee blades 36, 36. However, whenever the piston and cylinder assembly 56 is actuated the squeegee blades are alternately raised and lowered. With the construction described the squeegee blades 36, 36 can be raised and lowered independently of the movement of the squeegee carriage means 24.

In the construction described the adjustable manner in which the respective guide rails 18, 18 are supported from the rigid head frame 10 enables the rails 18, 18 to be adjusted to conform to the smoothness of the printing surface. In this manner the squeegee carriage means 24 riding on the rails 18 so adjusted will cause the squeegee carriage to traverse a printing stroke so that the pressure exerted by the squeegee blade 36 is maintained substantially uniform. This is because the adjustment of the rails 18 to the smoothness of the printing surface will cause the carriage to ride high over the high spots of the printing surface and low over the low spots, thus enabling the pressure of the squeegee to be maintained substantially constant. In this manner uniform penetration of color can be maintained in the event any unevenness should develop in the printing surface, and the rails 18 are adjusted accordingly.

The tilt mechanism defined also enables the chopper type squeegee operation to be utilized without the attendant traveling hardware heretofore required to manipulate the squeegee blades. This feature is particularly desirable in the larger machines where the squeegee is required to traverse a considerable distance.

While the invention has been described with respect to a particular embodiment, it will be understood and appreciated that variations and modifications may be made without departing from the spirit or scope of the invention.

What is claimed is:

1. A screen printing head for use with a screen printing machine having a printing surface for supporting thereon a material to be screen printed comprising:

a printing head frame having opposed longitudinally extending rigid support members,

a guide rail on each said support member, I

support means for supporting said guide rail on each of said rigid support members,

a squeegee carriage slidably mounted on said guide rails for traversing a printing stroke,

a squeegee carried on said squeegee carriage,

and said support means including means for adjusting the spacing between each said guide rail and the printing surface so that the pressure exerted by said squeegee is maintained substantially constant as said squeegee carriage traverses a printing stroke, said support means including a plurality of adjusting rods located at spaced intervals along said rigid members for supporting said guide rail from each said rigid support member,

said adjusting rods each having a threaded portion,

and an adjusting nut engaging said threaded portion whereby the adjustment of said nut on said adjusting rod adjusts each said guide rail relative to said printing surface.

2. The printing head screen defined in claim 1 wherein said guide rails comprise a round shaft, and said squeegee carriage includes a bearing slidably supporting said carriage on said shaft, said bearing circumscribing only a major circumferential portion of said shaft.

3. The printing head screen as defined in claim 1 and including:

a drive means for driving said carriage and squeegee carried thereon in traversing a printing stroke, and said squeegee including a pair of squeegee blades,

mounting means for mounting said squeegee blades on said carriage so that said squeegee blades are alternately moved between an operative and inoperative position,

and an actuating means for effecting the shifting of said squeegee blades alternately between operative and inoperative positions.

' 4. The invention as defined in claim 3 wherein said squeegee mounting means includes a rocker assembly,

and said actuating means being connected to said rocker assembly, and includes a flexible tilt drive,

for effecting the raising and lowering said squeegee blades between operative and inoperative positions accordingly,

and means for drivingly connecting said tilt drive to said carriage and squeegee drive means.

5. The printing head screen as defined in claim 4 wherein said squeegee carriage includes opposed carriage blocks slidably supported along the opposed slide rails,

said pair of squeegee blades extending between said carriage blocks,

said carriage drive means including an endless drive,

and a motor means connected to said endless drive for driving said endless drive,

and said means for drivingly connecting said tilt drive to said carriage and squeegee drive including a driving gear connected to said carriage drive means, and

a driven gear disposed in meshing relationship with said driving gear connected to said tilt drive.

6. The invention as defined in claim 5 wherein said actuating means includes a lever arm pivotally connected to said head frame,

said driven gear journalled to said lever arm,

a pair of idlers, said idlers being disposed on opposite sides of said driven gear and carried on said lever arm,

and said endless tilt drive being threaded about said idlers,

and an operating means for effecting the displacement of said lever arm whereby the displacement of said lever arm effects the alternate raising and lowering of said squeegee blade.

7. A printing head for use with a screen printing machine including a frame, a printing screen supported on said frame, squeegee carriage movably mounted on said frame for traversing a printing stroke, and a pair of squeegee assemblies mounted on said carriage, the improvement comprising:

a rocker assembly for supporting said squeegee on said carriage for alternate movement between a raised and lowered position relative to a printing screen,

a carriage drive means for effecting the drive of said carriage and squeegee for traversing a printing stroke,

an actuating means connected to said rocker assembly to actuate said assembly for raising and lowering the squeegees,

and means for drivingly connecting said actuating to said drive means,

and an operating means connected to said shifting means to operate said shifting means and thereby effect alternate movement of said squeegees between a raised and lowered position, said carriage drive means including:

an endless drive connected to said squeegee carriage,

a motor connected to said endless drive,

and said actuating means including an endless member connected to said rocker assembly for alternately raising and lowering sad squeegee blades,

said driving connection means including a driving gear connected to said carriage drive means, and

a driven gear meshing with said driving gear connected to said actuating means,

said actuating means further including a lever arm pivotally mounted on said frame means, said endless member interconnecting said lever arm to said rocker assembly.

and said operating means effecting the displacement of said lever arm to alternately raise and lower said squeegee beades accordingly.

8. A printing head for use on a screen printing machine comprising:

a printing head frame,

a printing screen supported on said frame,

opposed guide rails extending longitudinally of said frame,

a squeegee carriage slidably disposed along said rails,

said carriage including oppositely disposed carriage blocks slidably disposed along the opposed guide rails,

a rocker assembly connected to each carriage block,

said rocker assembly each including a rocker bar pivotally connected to said block,

an upper cross bar pivotally connected to a carriage block,

a pair of connecting links pivotally interconnected between the ends of said rocker bar and upper an idler sprocket journalled on said frame opposite said driven sprocket,

an endless flexible drive threaded over said driving sprocket and idler sprocket,

means connecting said flexible drive to said squeegee carriage,

a motor for driving said driving sprocket to effect the driving of said carriage means along said guide rail to traverse said printing stroke,

an actuating means connected to said rocker bar to effect the alternate raising and lowering of said squeegee blades relative to said screen,

said actuating means including a lever arm pivotally connected on said frame,

a spur rotatably journalled on said lever arm,

said spur gear and said driven gear being disposed in ing and lowering said squeegee blades accordingly. 

1. A screen printing head for use with a screen printing machine having a printing surface for supporting thereon a material to be screen printed comprising: a printing head frame having opposed longitudinally extending rigid support members, a guide rail on each said support member, support means for supporting said guide rail on each of said rigid support members, a squeegee carriage slidably mounted on said guide rails for traversing a printing stroke, a squeegee carried on said squeegee carriage, and said support means including means for adjusting the spacing between each said guide rail and the printing surface so that the pressure exerted by said squeegee is maintained substantially constant as said squeegee carriage traverses a printing stroke, said support means including a plurality of adjusting rods located at spaced intervals along said rigid members for supporting said guide rail from each said rigid support member, said adjusting rods each having a threaded portion, and an adjusting nut engaging said threaded portion whereby the adjustment of said nut on said adjusting rod adjusts each said guide rail relative to said printing surface.
 2. The printing head screen defined in claim 1 wherein said guide rails comprise a round shaft, and said squeegee carriage includes a bearing slidably supporting said carriage on said shaft, said bearing circumscribing only a major circumferential portion of said shaft.
 3. The printing head screen as defined in claim 1 and including: a drive means for driving said carriage and squeegee carried thereon in traversing a printing stroke, and said squeegee including a pair of squeegee blades, mounting means for mounting said squeegee blades on said carriage so that said squeegee blades are alternately moved between an operative and inoperative position, and an actuating means for effecting the shifting of said squeegee blades alternately between operative and inoperative positions.
 4. The invention as defined in claim 3 wherein said squeegee mounting means includes a rocker assembly, and said actuating means being connected to said rocker assembly, and includes a flexible tilt drive, for effecting the raising and lowering said squeegee blades between operative and inoperative positions accordingly, and means for drivingly connecting said tilt drive to said carriage and squeegee drive means.
 5. The printing head screen as defined in claim 4 wherein said squeegee carriage includes opposed carriage blocks slidably supported along the opposed slide rails, said pair of squeegee blades extending between said carriage blocks, said carriage drive means including an endless drive, and a motor means connected to said endless drive for driving said endless drive, and said means for drivingly connecting said tilt drive to said carriage and squeegee drive including a driving gear connected to said carriage drive means, and a driven gear disposed in meshing relationship with said driving gear connected to said tilt drive.
 6. The invention as defined in claim 5 wherein said actuating means includes a lever arm pivotally connected to said head frame, said driven gear journalled to said lever arm, a pair of idlers, said idlers being disposed on opposite sides of said driven gear and carried on said lever arm, and said endless tilt drive being threaded about said idlers, and an operating means for effecting the displacement of said lever arm whereby the displacement of said lever arm effects the alternate raising and lowering of saiD squeegee blade.
 7. A printing head for use with a screen printing machine including a frame, a printing screen supported on said frame, squeegee carriage movably mounted on said frame for traversing a printing stroke, and a pair of squeegee assemblies mounted on said carriage, the improvement comprising: a rocker assembly for supporting said squeegee on said carriage for alternate movement between a raised and lowered position relative to a printing screen, a carriage drive means for effecting the drive of said carriage and squeegee for traversing a printing stroke, an actuating means connected to said rocker assembly to actuate said assembly for raising and lowering the squeegees, and means for drivingly connecting said actuating to said drive means, and an operating means connected to said shifting means to operate said shifting means and thereby effect alternate movement of said squeegees between a raised and lowered position, said carriage drive means including: an endless drive connected to said squeegee carriage, a motor connected to said endless drive, and said actuating means including an endless member connected to said rocker assembly for alternately raising and lowering sad squeegee blades, said driving connection means including a driving gear connected to said carriage drive means, and a driven gear meshing with said driving gear connected to said actuating means, said actuating means further including a lever arm pivotally mounted on said frame means, said endless member interconnecting said lever arm to said rocker assembly. and said operating means effecting the displacement of said lever arm to alternately raise and lower said squeegee beades accordingly.
 8. A printing head for use on a screen printing machine comprising: a printing head frame, a printing screen supported on said frame, opposed guide rails extending longitudinally of said frame, a squeegee carriage slidably disposed along said rails, said carriage including oppositely disposed carriage blocks slidably disposed along the opposed guide rails, a rocker assembly connected to each carriage block, said rocker assembly each including a rocker bar pivotally connected to said block, an upper cross bar pivotally connected to a carriage block, a pair of connecting links pivotally interconnected between the ends of said rocker bar and upper cross bar, a squeegee support interconnected between corresponding opposed pairs of said connecting links, a squeegee blade connected to each squeegee support, a carriage drive means connected to said squeegee carriage for driving said carriage means and squeegee blades thereon along said guide rails to traverse a printing stroke, said carriage drive means including a drive shaft journalled adjacent one end of said frame, a driving sprocket connected to said shaft, a driven gear connected on said shaft, an idler sprocket journalled on said frame opposite said driven sprocket, an endless flexible drive threaded over said driving sprocket and idler sprocket, means connecting said flexible drive to said squeegee carriage, a motor for driving said driving sprocket to effect the driving of said carriage means along said guide rail to traverse said printing stroke, an actuating means connected to said rocker bar to effect the alternate raising and lowering of said squeegee blades relative to said screen, said actuating means including a lever arm pivotally connected on said frame, a spur rotatably journalled on said lever arm, said spur gear and said driven gear being disposed in meshing relationship, a sprocket coupled to said spur gear, idler sprockets disposed on opposite sides of said spur gear journalled to said lever arm, a rocker lever connected to said rocker bar, an endless member connecting said lever arm to said rocker lever, said endless member being threadEd over said spur gear coupled sprocket and idler sprockets on said lever arm whereby said endless member is driven in unison with said squeegee carriage drive means, and an operating means connected to said lever arm to effect the actuation thereof for alternately raising and lowering said squeegee blades accordingly. 